A Low-Power 28-Gb/s PAM-4 MZM Driver with Level Pre-distortion

We present a PAM-4 optical modulator driver for Mach-Zehnder modulator (MZM), having the level pre-distortion functionality so that the ratio of level mismatch (RLM) can be optimized. The driver employs a newly proposed PAM-4 stacked source-series terminated (SST) structure with impedance control so that it can provide high output voltage swing with low power consumption. A prototype chip including data generators and serializers is fabricated in 28-nm CMOS technology with 0.016 mm2 active chip area. With this, 28-Gb/s operation is achieved with 2.4 V differential output swing and 3.14 pJ/bit energy efficiency. It is experimentally demonstrated that our circuit can achieve larger than 95% RLM for a commercial LiNbO3 MZM PAM-4 modulation.